The Temporomandibular Joints themselves are the two joints on either side of the skull where the lower jaw is connected. The name itself comes from the names of the two bones being joined. The temporal bone is the lower section of the skull, while the mandible is the medical name for the lower jaw.

The joint's construction is similar to that of the spine, in that a disk of cartilage separates the two bones. The cartilage itself serves as a cushion between the bones, preventing painful friction that would occur if the two rubbed directly against each other, and also allows for easy rotational motion (the opening and closing of the jaw). However, the temporomandibular joint is also unique in several ways. First, the construction of the joint also allows for something known as translational motion: the ability to move the jaw from side to side and from front to back. In addition, this joint requires the use of two separate groups of muscles (the ones on both sides of the head) in order to move. And, this joint has one of the most severe restrictions on its motion. The opening of the joint is limited by the construction of the jawbone itself, while the closing is restricted by the teeth hitting.

This condition, also known as Temporomandibular Dysfunction (TMD) is a result of problems relating to the Temporomandibular Joint, the bones it connects, and the surrounding muscles. In general, it is due to some type of stress on the jaw (either acute or inherent) which in most cases results in the dislocation of the joint's cartilage disks or severe stressing of the muscles which move the lower jaw. The symptoms for the disorder are varied, and there is often overlap with the symptoms of other medical conditions. In general, however, TMD is characterized by the following symptoms:

More often than not, TMD itself will need to be diagnosed through the use of medical imaging because of the difficulty in using the symptoms alone in pinpointing TMD as the cause of the problem. Doctors can check for more than one of the symptoms in trying to diagnose the disorder (for example, if a patient comes in complaining of acute ear pain but does not have an ear infection, the doctor may listen for jaw popping or check for range of motion limitations in order to diagnose the problem as TMD), but again, these symptoms could also be due to other problems in the jaw, necessitating imaging of some sort. A panoramic X-Ray would allow a doctor to pinpoint a physical problem, such as a defect of the jaw, while an MRI or CT scan would aid in examining the joint itself.

TMD can be caused by a variety of things. One of the more obvious causes is a direct trauma to the jaw or head. Anything from being hit in the jaw to a severe case of whiplash can cause dislocation of the Temporomandibular Joint's cartilage or damage to its muscles. Inherent conditions can also lead to TMD. For example, a bad bite (an overbite, for example), can put stress on the joint and lead to TMD. Or, deformities in the jaw itself can lead to TMD. However, contrary to popular belief, nervous or stress conditions, like clenching of the jaw or constant gum chewing do not lead to TMD. However, they can aggravate an existing physical trigger (such as an overbite), leading to or accelerating the onset of TMD.

TMD can be treated in a variety of ways. If caught early, it is possible to (under a doctor's supervision or guidance) self-treat the condition by resting the joint through the eating of soft foods and avoiding gum, and relaxing the jaw muscles by avoiding clenching and using heating pads or hot water bags several times a day. However, in many cases, more complicated treatments are needed. Some TMD patients may require the assistance of a physical therapist to help repair the joint. An occusal splint may also be necessary to help prevent future damage to the joint. In cases where the TMD sufferer has a physical condition that led to the disorder, oral corrective surgery may be called for. Often, these more serious medical treatments will also be accompanied by the self-treatments mentioned initially.

Unlike TMD, which is a physical condition, Temporomandibular Joint Disease is an actual disease. Often, this condition is simply rheumatoid arthritis or osteoarthritis of the jaw or joint area. However, because the symptoms for Temporomandibular Joint Disease are oftentimes the same as those of TMD, the disease is usually mistaken for the disorder. In the case of osteoarthritis, the cartilage disk between the jaw and skull (the one that would have been dislocated in TMD) has actually deteriorated to the point that the two bones are rubbing to such an extent as to cause pain or a limitation in range of motion. If rheumatoid arthritis is the cause, the body's immune system is mistakenly attacking the joint tissue itself.

TMJ disease can be treated in the same manner as any other arthritis condition, through medication and physical therapy. The most common medical treatments are common painkillers such as Advil or Aleve (NSAIDs) or steroids like glucocorticoids. In extreme cases, joint replacement or other surgeries are an option, though these are usually reserved for cases where the arthritic condition occurs in joints such as the hip or knee.